This study investigates the pressureless infiltration of 3D-printed alumina with copper oxide to produce ceramic composites suitable for ASML application. ASML’s components demand high mechanical performance ceramics with complex shapes and low porosity. An effective method for producing large and complex shapes is powder bed binder jetting (PBBJ). A major challenge of this technique is achieving a low level of porosity. To address this challenge, pressureless infiltration has been employed as a post-processing method to reduce porosity. Alumina porous structures with a relative bulk density of 59% were fabricated with PBBJ. An infiltration setup was designed and successfully tested on these alumina porous structures. Infiltrating the alumina with copper oxide in an oxygen-rich environment, resulted in a relative density of 85% and a flexural strength of 53.6 MPa. Reactions between alumina and copper oxide resulted in the consumption of up to 50% of the alumina, leading to the formation of ternary oxides (like CuAlO₂). The ternary oxides accounted for approximately 70 wt.% of the composite. The formation of these ternary oxides significantly reduces the composite’s mechanical properties, as it consumed the load bearing alumina. It was predicted that at 0% porosity, the theoretical minimal strength of this composite would be only 33% of the strength of alumina. The feasibility of infiltration in nitrogen was explored through differential thermal analysis (DTA), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) analyses. For these tests an equimolar powder mixture (consisting of Al₂O₃ and Cu₂O) was used. The results revealed 5 different phase transitions during the infiltration cycle. Even under the most optimal thermal infiltration conditions, 72 wt.% ternary oxide was formed. Pressureless infiltration shows potential in improving the density of porous bodies created by PBBJ. The thermal infiltration cycle has to be improved in order to minimize the unwanted reactions between alumina and copper oxide. Using alternative materials for infiltration, may better meet ASML’s requirements.